1. Field of the Invention
The present invention relates to processes making it possible to lock smart or chip cards, essentially for the purpose of preventing fraudulent use thereof.
2. Description of the Prior Art
Smart or chip cards are very frequently used in applications, e.g. banking, requiring a high level of security against fraudulent use. Fraudulent use can not only take place by a thief, but also by the owner of the card. Thus, in different stages, such as the production of the chip, transportation, personalization, etc. which precede the delivery of the card to the customer, gradually the field of action of a component (the chip) is limited, because at the outset it can lave numerous possible uses. If he were able to recommence the stages in upstream form, the card holder could use the card for purposes for which this is not authorized, e.g. for making multiple withdrawals from a bank, or exceeding the limit granted.
It is known to prevent such uses by locking each of the stages by logic locks, which make it impossible to recommence the operations corresponding to these stages. These locks are generally formed by a bit (or a word) written in the non-volatile memory (EPROM or EEPROM) of the circuit of the card at the end of the stage taking place. The program corresponding to this stage tests, prior to starting up, the presence of this bit and only starts if the latter has been recognized.
This solution is not completely satisfactory, because it can occur that such locks are accidentally moved aside or erased.
In addition, during the starting up of the system on energizing the card, there is necessarily an initialization phase making it possible for criminals to neutralize the volatile memory (RAM) and override the locking system.
Finally, it is not possible to completely test the component of the card at the end of its manufacture, because this would involve activating the locks and would make it impossible to return backwards in order to supply the card manufacturer with non-personalized components. It is therefore necessary to test the component and then the card at each stage between the manufacture of the component by successively setting the locks.